The present invention, as illustrated by its many embodiments, relates primarily to a geosynthetic-reinforced segmental retaining wall (SRW). The components of a wall illustrated herein include a geosynthetic reinforcement loaded at one end and in contact with a locking bar at an opposite end. The locking bar and a section of the geosynthetic reinforcement are then captured between lower and upper segmental units. Such a wall is able to realize the long-term design strength of the geosynthetic reinforcement because the locking bar rotates to engage and hold the entire width of the geosynthetic reinforcement to an interior surface of the segmental units which comprise the wall.
The building construction and land development industry requires retaining walls to stabilize substantially vertical sections of earth. Retaining walls can be constructed on-site with poured-in-place concrete or assembled on-site with various segmental units. One type of assembled wall is constructed with pre-manufactured blocks stacked to form an exposed wall face. In practice, a connector is typically located between vertical courses of stacked block and is integral with a solid anchor embedded in the backfillxe2x80x94the tamped earth immediately adjacent to the stacked blocks. The anchor and connector effectively unify the backfill and stacked blocks to create the retaining wall. U.S. Pat. No. 5,921,715 is representative of traditional anchors and connectors.
Recently, improved reinforced-earth systems have emerged as low cost alternatives to the above wall assemblies. In these improved systems the soil is reinforced with geosynthetics; materials made typically from high-tenacity polyester, polypropylene, and high-density polyethylene. Polyester and polypropylene geosynthetics are usually woven into a relatively flexible and dimensionally stable grid or textile matrix. They are referred to as xe2x80x9cgeogridsxe2x80x9d and xe2x80x9cgeotextilesxe2x80x9d, respectively. Polypropylene and high-density polyethylene are also used to manufacture relatively stiff geogrids using an extrusion-based process. As will be understood by those skilled in the art, geosynthetic reinforcements may be xe2x80x9cstiffxe2x80x9d or may be xe2x80x9cflexible.xe2x80x9d
The designer of a geosynthetic-reinforced earth retaining wall must consider the strength of the connectionxe2x80x94the point at which forces exerted on the segmental unit are transferred to the geosynthetic reinforcement. An objective of the designer is to minimize the relative displacement between the geosynthetic reinforcement and the segmental units. By minimizing the relative displacement, the possibility of bulging, leaning, and other types of undesirable wall movement is reduced. The relative displacement can be reduced by a connection between the unit and reinforcement. Forces which tend to create the displacement include those exerted by soil at the back of the units and those which develop in the plane of the geosynthetic reinforcement. If the forces at the back of the unit can be transferred to the geosynthetic via a connection, the total relative displacement between the unit and geosynthetic can be significantly reduced. Therefore, the strength of the connection between the unit and geosynthetic govern the magnitude of the reduction in relative displacement. Using prevalent standard practice, the relative displacement is reduced to acceptable levels when the peak strength at the connection of the geosynthetic reinforcement and segmental retaining wall unit exceeds the horizontal stress applied to the back of the segmental unit.
If it is not possible with a given type of unit and geosynthetic to develop a connection strength which exceeds the horizontal stress, then the magnitude of the horizontal stress must be reduced. This reduction can be accomplished by decreasing the vertical space between layers of geosynthetic reinforcement. However, a decrease in distance between layers of reinforcement equates to more layers of reinforcement, and results in higher reinforcement costs.
Another objective of the designer is to limit tensile stresses in the plane of the geosynthetic reinforcement to levels below the material""s long-term design strength (LTDS). The magnitude of these stresses are a function of geosynthetic reinforcement spacing, soil strength, wall height, and load conditions at the top of the wall. A reinforcement design which is optimal with respect to geosynthetic costs is one in which the LTDS of the geosynthetic exceeds the calculated stresses in the geosynthetic by an amount deemed to provide an adequate factor to safety against tensile rupture.
Thus, the design of the geosynthetic reinforcement for a segmental retaining wall system is primarily controlled by two factors: 1) the peak connection strength between the segmental units and the geosynthetic reinforcement; and 2) the LTDS of the geosynthetic reinforcement. If the peak connection strength is less than the LTDS of the geosynthetic, the connection strength is said to control the reinforcement design. If the peak connection strength is greater than the LTDS of the geosynthetic, the geosynthetic strength is said to control the reinforcement design.
For most combinations of segmental retaining wall units and geosynthetic reinforcement available in today""s market, peak connection strength controls the reinforcement design for wall heights in excess of 10 to 15 feet. This limitation exists because the walls rely on one of two mechanisms, or a combination of both, to connect geosynthetic reinforcement to segmental units: 1) friction between the reinforcement and the segmental units; and 2) a dowel which is inserted into the lower and upper segmental units.
For frictional systems, the strength of the connection depends on the coefficient of friction between the geosynthetic and the segmental unit and the normal load applied at the frictional interface. At low to medium normal loads, failure of the connection usually occurs because the reinforcement slips between the segmental units. At high loads, the geosynthetic is often damaged and weakened as slips between the segmental units, and it may fail and rupture.
For dowel-based systems, the dowel passes through an aperture in geogrid reinforcement or between yarns in a geotextile reinforcement. Connection failure of flexible geogrids in dowel systems typically occurs when traverse geogrid members displace or rupture as they pull against the dowel. Similarly, connection failure of geotextiles in dowel systems typically occurs when yarns tear or displace as they pull against the dowel.
To compensate for the relatively inefficient connection of most geosynthetic reinforcement-segmental unit combinations, relatively frequent spacing of geosynthetic reinforcement is required. Because a relatively large amount of geosynthetic material is involved, these combinations can be inefficient with respect to cost. An optimized design is one in which the peak connection strength exceeds the LTDS required of the geosynthetic reinforcement.
It is known to provide a reinforced-earth retaining wall assembled from stacked blocks, which includes a connector bar positioned between vertical courses of block. The connector bar comprises a base and a series of spaced keys that project vertically. The connector bar is positioned in a channel of a lower block, and a geogrid is laid over the bar so as to hook a transverse member around each key. The geogrid is then extended laterally from the connector into the adjacent backfill. An upper block is then stacked over the connector bar to complete the connector assembly.
It is also known to construct a reinforced-earth retaining wall by providing a geosynthetic reinforcement wrapped around a solid body anchor located within a segmental unit. For example, a trough receives an anchor wrapped in a geotextile wherein the trough is then loaded with backfill. Alternatively, the trough may receive an anchor wrapped in a geotextile wherein the anchor is then mechanically fastened to the trough before the trough is loaded with backfill.
Another reinforced-earth retaining wall provides a flexible polymer sheet anchor that is connected to an assembly of stacked blocks by wedging one end of the sheet into a slot located within the blocks. In this example, the sheet is laid in the slot followed by a wedging element that is hammered into the slot. The wedging element forces and holds the sheet against the bottom and walls of the slot.
The primary thrust of the prior art reinforced-earth components and methods is to construct a retaining wall using oversized stackable modules or specially manufactured components. In the former case, wall construction requires operator driven machinery capable of lifting heavy weights. In the latter case, wall construction requires labor intensive assembly of many small components. Further, by connecting to individual transverse members of the geosynthetic reinforcement, the prior art walls are unable to utilize the long-term design strength of the geosynthetic reinforcement. Also, the prior art components and methods require the anchor and wall connection be tightly fitted and locked during assembly. For example, a flexible sheet is hammered into a slot or a transverse member is hooked to a dowel. Finally, prior art components, specifically the segmental units, include edges and projections which often function to tear or rupture the geosynthetic reinforcement.
When geosynthetic reinforced segmental retaining walls are constructed, soil is compacted behind the segmental units on top of layers of geosynthetic reinforcement in xe2x80x9cliftsxe2x80x9d of 6 to 12 inches. Builders typically attempt to make the top of a soil lift level with the top of an adjacent segmental unit before installing a layer of geosynthetic reinforcement. However, this condition is very difficult to obtain. Usually, the elevation at the top of the soil lift is below the top of the adjacent segmental unit. When a layer of geosynthetic reinforcement is installed on the segmental unit and extended into the soil zone, it contours to the top of the unit and top of the soil lift, bending around the top rear corner of the segmental unit. As the wall height increases, soil adjacent to the back of the segmental units tends to settle slightly. The settlement applies tension to the portion of the geosynthetic in contact with the top rear corner of the segmental unit.
Currently, many types of segmental retaining wall units have a geometry such that the plane at the top and rear of the unit intersect at an angle of 90 degrees. In walls constructed with these units, the geosynthetic reinforcement extends from between the stacked units, turns downward at the back of the unit, and then extends into the reinforced soil zone. Where the geosynthetic turns around the top rear corner of the block, a concentration of shear stresses develop in the geosynthetic. Existing design and testing methodologies do not consider the development of these stresses, yet they are present in virtually all geosynthetic-reinforced segmental retaining wall structures. The development of the stresses may cause rupture in the geosynthetic reinforcement.
Thus, there exists a need for a reinforced-earth retaining wall which is constructed of hand-stackable modules; which is constructed from a minimum number of readily available components; which includes a connector that utilizes the long-term design strength of the geosynthetic reinforcement; which evenly distributes the load of the backfill across the width of the wall; which eliminates concentrated stresses within the components; which does not require the anchor and wall connection be tightly fitted and locked during assembly, and which provides components which do not pose a threat of rupture to the geosynthetic reinforcement.
The present invention, in one or more of its illustrated embodiments, seeks to cure the problems and prior art inadequacies noted above by providing a reinforced-earth retaining wall that is easy to construct and is able to utilize the long-term design strength of the geosynthetic reinforcement anchor.
In accordance with the present invention, this objective is accomplished by providing the components and a method of constructing a reinforced-earth retaining wall, comprising: a multifaceted rotatable locking bar in contact with one end of a geosynthetic reinforcement; a lower block with an edgeless surface section adjacent to a receiving channel which accepts the locking bar and geosynthetic reinforcement; and, an upper block with a receiving channel which also accepts the locking bar and geosynthetic reinforcement. With a load applied to an opposite end of the geosynthetic reinforcement, the forces exerted by the load are transferred via the geosynthetic reinforcement to the locking bar, causing the bar to rotate and engage the geosynthetic reinforcement with at least one side of a receiving channel.
Generally described, the present invention comprises a lower block, an upper block, a rotatable locking bar positioned between the blocks, and a geosynthetic reinforcement in contact with the locking bar. The lower block includes at least an upper receiving channel and an edgeless top surface. From the rear of the lower block to the upper receiving channel, inclusive, the top surface does not include an identifiable edge that could threaten or rupture the geosynthetic reinforcement. The upper block may include a lower receiving channel, but it is not required. When stacked, the lower and upper receiving blocks form a receiving conduit.
In practice, a lower block is set and a geosynthetic reinforcement is laid over the top surface and upper receiving channel. Thereafter, the locking bar is positioned within the receiving channel, over the geosynthetic reinforcement. The geosynthetic reinforcement is then looped back over to rest on top of the locking bar. Next, the upper tier block is placed over the lower block to form a receiving conduit which fully encapsulates the locking bar and a section of the geosynthetic reinforcement.
In one embodiment, the receiving conduit is wider than the combination of the locking bar and wrapped geosynthetic reinforcement.
In another embodiment, the geosynthetic reinforcement is laid over the upper surface and upper receiving channel. The locking bar is then positioned within the upper receiving channel but the geosynthetic reinforcement is not wrapped back over the locking bar. Rather, it is permitted to extend past the receiving channel a short distance. Next, the upper tier block is placed over the lower block to form a receiving conduit which fully encapsulates the locking bar and a section of the geosynthetic reinforcement.
The geosynthetic reinforcement is extended behind the wall face into the adjacent soil mass and tensioned. As the wall height is increased, additional tension develops in the geosynthetic reinforcement. Also, horizontal earth stresses develop at the back of the segmental retaining wall units. Tension in the geosynthetic and pressure at the back of the segmental unit produces a relative displacement between these components. The displacement results in rotation of the locking bar in the receiving conduit. There, it binds the geosynthetic between the bar and the conduit walls. Once bound, stresses at the back of the segmental unit are transferred to the geosynthetic reinforcement and subsequent relative displacement between the unit and geosynthetic is eliminated or reduced to insignificant levels.
As the geosynthetic exits the receiving conduit, it presses against the edgeless surface section adjacent to the conduit. Because the surface is edgeless, no concentrated shear stresses are applied to the geosynthetic.
In practice, the combination of a geosynthetic reinforcement and rotatable locking bar filly utilizes the LTDS of the geosynthetic reinforcement because the locking bar is in full contact with the entire width of the geosynthetic reinforcement along all points. The full LTDS of the geosynthetic can be used because the peak connection strength exceeds the LTDS. The connection strength increases as the tensile stress in the reinforcement increasesxe2x80x94that is, the higher the stress, the more force with which the rotating bar binds the geosynthetic.
The geosynthetic does not pass over an edge adjacent to the receiving conduit or at the back of the segmental unit where high shear stress would develop and cause premature rupture. Because of these features, optimized reinforcement design with respect to geosynthetic cost is possible.